The Design,Fabrication And Characteristics Of Self-healable Strain Sensors

Strain sensors are widely used in wearable devices and healthcare diagnosis due to their excellent force sensitivity.However,in practical use,excessive use,friction,and collision cause mechanical damages and performance degradation of strain sensors,which greatly affects the application of strain sensors.Self-healing strain sensor is a device,which can measures the strain generated by external force and introduces self-healing properties.And its performance and application mainly depend on self-healing materials/conductive materials.At present,self-healing materials mainly achieve self-healing of materials through two kinds of repairing methods: extrinsic and intrinsic type,and these selfhealing materials are divided into hydrogel and elastomer in flexibility.In view of the fact that the self-healing elastomer materials have better stability and strain sensitivity than the self-healing hydrogel materials,the "sandwich" self-healing strain sensors were prepared based on the self-healing elastomer materials,its mechanical properties,electrical properties and self-healing ability were studied.The main works of the thesis are as follows.(1)Based on the characteristics of good transparency,strong Young's modulus and good mechanical properties of PDMS,Poly(acrylic acid)-hydroxyl-terminated polydimethylsiloxane(PAA-PDMS)elastomers with transparency,self-adhesiveness and self-healing ability were fabricated by chemical one-step reaction.Study of mechanical properties by adjusting the ratio of PAA to PDMS-OH And self-healing performance to further select the best ratio of good performance.Through the exploration of characterization analysis,mechanical properties and self-healing performance experiments,the experimental results show that the mechanical properties of PAA-PDMS elastomers decrease with the increase of PAA ratio,while the repair performance is reversed.PAA-PDMS elastomer exhibits the best performance,such as good mechanical tensile strength(0.383 MPa),good tensile length(94.5%),short self-healing time(?10 s)and High self-repairing efficiency(98%)and gentle self-healing conditions do not require excitation from external conditions when the ratio of PAA:PDMS-OH is 3:1.In addition,the PAA-PDMS elastomer encapsulated polyethyleneimine-reduced graphene oxide(PEI-rGO)layer was applied to the strain sensors and its performance was explored due to the good self-adhesiveness of the PAA-PDMS elastomers.(2)Based on the good conductivity,large specific surface area,high Young's modulus and good mechanical properties of graphene,polyacrylic acid(PAA)and graphene oxide(GO)were used to prepare polyacrylic acid-reduced graphene oxide.(PAA-rGO)selfhealing conductive elastomer.The effects of different ratios of PAA and GO on the mechanical properties,electrical properties and self-healing properties of PAA-rGO conductive elastomers were discussed.The experimental results show that the PAA-rGO conductive elastomer with PAA:GO of 20:1 exhibits excellent mechanical properties(tensile length 187.4%,tensile strength 0.548 MPa)and electrical properties(response of 3.71 at 20% strain and gague factor is 18.5),self-healing performance(repairing time : ?30 s under room temperature,self-healing efficiency: 96%).In addition,the healed PAArGO conductive elastomers has a stable response under strain after stretching for 500 times.After three cutting/healing cycles,the PAA-rGO conductive elastomer had a strain factor of 56 at 20% strain and the test was stable.(3)Self-healing strain sensors(PAA-PDMS/PAA-rGO sensors)were prepared by self-assembly process between the PAA-rGO self-healing elastomer and PAA-rGO selfhealing conductive elastomers.The mechanical properties,strain properties and selfhealing properties of the “sandwich” self-healing strain sensors were investigated and compared.After the PAA-PDMS/PAA-rGO sensors were cut three times at the same position,its mechanical properties and electrical properties still maintained good selfhealing efficiency(> 96%),and even restored to 83% after 10 times repeated self-healing cycles.In summary,the self-healing strain sensors based on “sandwich” structure have better mechanical properties,electrical properties and self-healing efficiency than selfhealing conductive PAA-rGO elastomers than single conductive elastomer layer.